<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .list {
            width: 200px;
            height: 150px;
            background-color: skyblue;
            overflow: auto;
        }

        .news {
            height: 30px;
        }
    </style>
</head>
<body>
<!--准备好一个“容器”-->
<div id="test"></div>

<!--引入react核心库-->
<script type="text/javascript" src="../newjs/react.development.js"></script>
<!--引入react-dom，用于支持react操作DOM -->
<script type="text/javascript" src="../newjs/react-dom.development.js"></script>
<!--引入babel，用于将jsx转为js -->
<script type="text/javascript" src="../newjs/babel.min.js"></script>

<script type="text/javascript" src="../newjs/prop-types.js"></script>

<script type="text/babel">
    class NewsList extends React.Component {
        state = {newsArr: []}

        componentDidMount() {
            setInterval(() => {
                const {newsArr} = this.state
                const news = '新闻' + (newsArr.length + 1)
                this.setState({newsArr: [news, ...newsArr]})
            }, 1000)
        }

        getSnapshotBeforeUpdate() {
            return this.refs.list.scrollHeight
        }

        componentDidUpdate(preProps,preState,height){
            this.refs.list.scrollTop += this.refs.list.scrollHeight - height
        }

        render() {
            return (
                <div className="list" ref="list">
                    {
                        this.state.newsArr.map((n, index) => {
                            return <div key={index} className="news">{n}</div>
                        })
                    }
                </div>
            )
        }
    }

    //2.渲染组件到页面
    ReactDOM.render(<NewsList></NewsList>, document.getElementById('test'))
</script>
</body>
</html>

